1. Technical Field
The present invention relates to a communication apparatus, a communication system, a communication method, an integrated circuit and a circuit module capable of improving estimation precision of effective communication rates when the effective communication rates are estimated using the results of a transmission channel estimation performed between power line communication apparatuses without communication apparatuses for carrying out actual data communication.
2. Background Art
A communication network such as a wireless LAN or a power line communication network permits communication between a plurality of communication apparatuses. In the case of a power line communication (PLC), a PLC modem and the like can be employed as the communication apparatus. There is used a method of using a master communication apparatus carrying out network management or a method of carrying out communication between slave communication apparatuses without using the master communication apparatus. Generally, at least two communication apparatuses communicate with each other in either method. A communication performance between the two communication apparatuses depends on the state of a transmission channel (a power line in the case of the power line communication). The communication performance may deteriorate when an electrical or electronic factor such as a noise causing signal attenuation of the transmission channel exists. In a case of wireless communication, the communication performance may also deteriorate since a signal attenuates due to physical factors such as a wall blocking radio waves. As the physical factors over the power line which affect the communication performance in the power line communication, there are exemplified signal attenuation caused by reflected waves of signals generated due to branch of lines and signal attenuation caused by an connecting to another single phase wiring, that is, an (L1 phase)/(L2 phase) wiring in a distribution board collecting power lines of a house.
In a known power line communication, in order to carry out high-performance communication while miniaturizing an influence on signals, a transmission channel estimation of measuring the communication performance of the transmission channel between the communication apparatuses is performed and communication is carried out using a common transmitting and receiving tone map between the communication apparatuses on the basis of the results of the transmission channel estimation (for example, see Patent Document 1 and Patent Document 2). It is possible to obtain the theoretical best communication rate from the tone map obtained from the results of the transmission channel estimation.
Details of the transmission channel estimation performed in the known power line communication will be described with reference to FIG. 9.
FIG. 9 is a diagram illustrating a method of estimating an effective communication rate from the results of the transmission channel estimation.
In this method, the transmission channel estimation is performed plural times (twelve times), an average value of PHY rates from the results of the transmission channel estimation performed plural times is calculated, and the effective communication rate (a TCP rate or a UDP rate) is calculated from the average value of the PHY rates.
A relationship between the PHY rate and the effective communication rate has a static characteristic. Accordingly, once the PHY rate is determined, the effective communication rate is uniquely determined. In the example shown in FIG. 9, since an average PHY rate≈27 Mbps, a TCP rate≈13 Mbps and a UDP rate≈17 Mbps are estimated with reference to a predetermined relationship.
[Patent Document 1] JP-A-2005-253047
[Patent Document 2] JP-A-11-163807
However, the known power line communication has a problem in that the power line may generate a periodic noise synchronized with a commercial power supply over the power line communication network in accordance with a use environment of the power line when a specific household electronic appliance or the like is connected to the power line.
FIG. 32 is a flowchart illustrating a known estimation process of estimating the effective communication rate. In the estimation method illustrating in FIG. 32, the transmission channel estimation is performed defined plural times (N times) to obtain the plural (N) results (PHY rates) of the transmission channel estimation, while performing a timeout process of the transmission channel estimation which determines whether the results of the transmission channel estimation are returned within a predetermined period (Step S1401). Subsequently, an average value is calculated from the plural (N) PHY rates obtained in Step S1401 (Step S1402).
Subsequently, the average value of the PHY rates obtained in Step S1402 is set as the PHY rate used for the estimation of the effective communication rate (Step S1403). Finally, a practical communication rate is estimated from the PHY rate used for the estimation of the effective communication rate obtained in Step S1403 (Step S1404).
However, when a specific household electronic appliance (for example, a microwave oven, a drier, an electrical cleaner, etc.) is connected through the power line, a noise caused by the household electronic appliance may occur in the power line communication network. The periodic noise synchronized with a power frequency generally occurs.
The results (PHY rates) of the transmission channel estimation become smaller than the average value of the PHY rates, when the transmission channel estimation is performed plural times (N times) in synchronization with this noise.
Therefore, the estimation of the effective communication rate on which the noise reflects is not satisfactorily performed, since the value of the effective communication rate estimated using only the average value of the PHY rates is different from the value of the actual effective communication rate between the communication apparatuses during the occurrence of the noise.
In particular, communication is carried out on the basis of communication protocols (for example, TCP) in an actual communication apparatus (for example, a personal computer or an IP phone) connected to a device. However, the communication is carried out in accordance with the rule of restraining the effective communication rate to be low, when a loss of communication data occurs due to the noise over the transmission channel. Accordingly, when the noise occurs, there occurs a problem in that a difference between the estimation value and the measurement value of the effective communication rate become large.
In order to estimate the effective communication rate on which the periodic noise reflects, timing at which the transmission channel estimation is performed is also important. In the known transmission channel estimation, the values of the PHY rates obtained by the transmission channel estimation did not sufficiently reflect the occurrence of the periodic noise, since the transmission channel estimation is performed at timing which does not related to timing at which the periodic noise occurs.
A location (outlet) where the power line communication apparatus is connected is important in construction of the power line communication network. A construction work of the power line communication network is facilitated when the effective communication rate between the power line communication apparatuses is estimated precisely in advance before the construction of the power line communication network.